The present invention relates to a vehicle that may be braked with a motor as well as with a mechanical brake utilizing a frictional force, and also to a method of controlling such a vehicle. More specifically the present invention pertains to a vehicle that is braked with a motor to attain an arbitrarily adjustable speed reduction rate, as well as to a controlling method to actualize such braking.
A hybrid vehicle with both an engine and a motor as the power source has been proposed as one form of vehicles. For example, a hybrid vehicle disclosed in JAPANESE PATENT LAID-OPEN GAZETTE No. 9-37407 additionally has a motor placed in series between an engine and a transmission in a power system of an ordinary vehicle where an output shaft of the engine is connected with a drive shaft via the transmission. This arrangement enables the hybrid vehicle to be driven by means of both the engine and the motor as the power source. The engine generally has poor fuel consumption at a time of starting the vehicle. In order to avoid the driving of poor fuel consumption, the hybrid vehicle makes a start by utilizing the power of the motor. After the speed of the vehicle reaches a predetermined level, the hybrid vehicle starts its engine and is subsequently driven by utilizing the power of the engine. The hybrid vehicle accordingly improves the fuel consumption at the time of starting. The hybrid vehicle causes the motor to regenerate the rotations of the drive shaft as electric power, which is used for braking (hereinafter such braking is referred to as the regenerative braking). The hybrid vehicle carries out the regenerative braking and thereby enables the kinetic energy to be used without significant wastes. These characteristics desirably improve the fuel consumption of the hybrid vehicle.
There are two different types of braking in the vehicle. One braking process presses a brake pad against the drive shaft in response to actuation of a brake pedal, so as to apply a frictional force to the axle (hereinafter referred to as the wheel braking). The other braking process causes the power source to apply a load to the drive shaft, like engine brake (hereinafter referred to as the power source braking). The hybrid vehicle utilizes, as the power source braking, engine brake based on a pumping loss of the engine and regenerative braking due to a regenerative load of the motor. The power source braking does not require the driver to change the foot position from the accelerator pedal to the brake pedal for the purpose of braking. In order to enhance the effectiveness of the power source braking, it is desirable to arbitrarily set a speed reduction rate required by the driver.
The engine brake results in a substantially fixed speed reduction rate according to the engine speed, unless the open and close timings of an intake valve and an exhaust valve are changed. In order to attain a desired speed reduction rate by engine brake, the driver is required to operate a gearshift level to vary the gear ratio of the transmission and thereby change the ratio of the torque of the power source to the torque output to the drive shaft. The advantage of the regenerative braking of the motor is, on the other hand, relatively easy control of the regenerative load, which leads to relatively easy control of the speed reduction rate.
In the conventional hybrid vehicles, however, a diversity of problems as discussed below arise in the braking process utilizing the motor.
The first problem is that there has been no discussion on the possible range of the speed reduction rate set by the driver. Namely no discussion has been held on the desirable range of the speed reduction rate, in order to attain the stable driving of the hybrid vehicle.
The second problem is that the speed reduction rate can be set only in a variable range of the regenerative load of the motor. In some cases, the hybrid vehicle can not sufficiently attain the speed reduction rate required by the driver. The insufficient speed reduction rate occurs especially in the course of high-speed driving of the vehicle.
The third problem is that the driving state allowing the regenerative braking with the motor is relatively limited. For example, when the accumulator is in a state close to the full charge level, no further charging is allowed for the regenerative braking.
In such circumstances, the advantages of the power source braking, for example, actuation of braking without any change the foot position, are not fully utilized.
Utilizing the wheel braking to compensate for the insufficiency of the speed reduction rate damages the advantage of the power source braking that does not require any change of the foot position. The wheel braking causes the kinetic energy of the vehicle to be consumed in the form of thermal energy and accordingly damages the advantage of the hybrid vehicle that is the effective use of energy.
In the prior art hybrid vehicle, a large speed reduction rate may be attained by operating the gearshift lever to change the gear ratio of the transmission. In this case, however, the speed reduction rate drastically varies with the operation of the gearshift lever, which results in a poor ride..
The fourth problem is that there has been no discussion on the manipulation mechanism that allows the user to set the speed reduction rate. For the effective actuation of the regenerative braking, it is desirable that the user can arbitrarily and readily set the speed reduction rate. The desired speed reduction rate frequently varies according to the driving state of the vehicle, so that the easy change of the settings is demanded. It is, on the other hand, demanded to prevent an unintentional variation in speed reduction rate. No manipulation mechanisms for allowing the user to set the speed reduction rate have practically been proposed by considering such conditions.
The fifth problem is that there has been no discussion on the desired settings of the speed reduction rate at the respective gear ratios in response to the operation of the gearshift lever to change the gear ratio and the specification of the speed reduction rate. In order to fully utilize the advantage of the power source braking that does not require any change of the foot position from the accelerator pedal to the brake pedal and enhance the operatability of the hybrid vehicle, it is required to attain the speed reduction rate that well follows the driver""s feeling. There has been no discussion from these viewpoints how the setting of the speed reduction rate should vary against the changing gear ratio, for example, in response to the specification of the speed reduction rate by the driver. In the prior art hybrid vehicles, there is still a requirement for the further improvement in effectiveness of the power source braking.
The sixth problem is that the energy recovery rate is lowered when the driver operates the gearshift lever to changeover the working range of the gear ratio. In the hybrid vehicle with a transmission, the driver operates the gearshift lever with a view to gaining a greater speed reduction rate and ensuring quick acceleration after the braking control. The driver may select a specific gearshift position where the positions of the change-speed gear having the greater gear ratios are available. In other words, the driver may select the gearshift position that prohibits the use of the positions of the change-speed gear having the smaller gear ratios.
In the prior art hybrid vehicle, the quantity of regeneration by the motor is reduced in such cases. This leads to the insufficient regeneration of the kinetic energy of the vehicle in the form of electric power.
In order to enhance the energy recovery rate of the vehicle, the braking control may be carried out at another specific gearshift position where the positions of the change-speed gear having the smaller gear ratios are available. This leads to a lesser ratio of the speed reduction rate applied to the axle to the braking torque of the power source. Due to this lesser ratio, the braking control by the power source braking can not be implemented with the sufficiently large speed reduction rate desired by the driver. The driver should accordingly use the wheel braking to obtain the sufficient speed reduction rate. The use of the wheel braking leads to the lowered energy recovery rate. The selection of this gearshift position does not allow the quick acceleration desired by the driver after the braking control, thereby significantly damaging the controllability of the vehicle.
The problems discussed above arise not only in the hybrid vehicles with both the engine and the motor as the power source but in any vehicles with only the motor as the power source. Similar problems are also found in vehicles with both the engine and the motor mounted thereon; which uses only the engine for the power source of drive and utilizes the motor for other purposes, such as regenerative braking.
One object of the present invention is to provide a vehicle that attains adequate speed reduction according to driving conditions of the vehicle by utilizing a motor, and a method of controlling such a vehicle. Another object of the present invention is to provide a vehicle that smoothly regulates a speed reduction rate in a process of braking with a motor in a wide possible range of setting in response to an instruction of a driver, and a controlling method to attain such braking.
At least part of the above and the other related objects is attained by a first vehicle that includes a motor, a transmission that enables selection of a plurality of gear ratios in a process of power transmission, and a drive shaft, which are connected with one another, and is braked by means of a torque output from the motor. The first vehicle includes: an operation unit, through an operation of which a driver of the vehicle specifies a speed reduction rate in a process of braking with the motor; a target speed reduction rate setting unit that sets a target speed reduction rate in response to the operation of the operation unit; a selection unit that selects a target gear ratio among a plurality of available gear ratios, the target gear ratio enabling the currently set target speed reduction rate to be attained by the torque of the motor; a motor driving state specification unit that specifies a target driving state of the motor, in order to enable a braking force that attains the currently set target speed reduction rate to be applied to the drive shaft; and a control unit that controls the transmission to attain the target gear ratio and drives the motor in the specified target driving state.
The target driving state of the motor is specified by a diversity of parameters relating to driving conditions, for example, the target torque, the electric power regenerated by the motor, and the electric current flowing through the motor.
In the vehicle of the present invention, the selection unit selects an adequate gear ratio according to the speed reduction rate specified by the driver and the magnitude of the torque output from the motor. Controlling the driving state of the motor at the adequate gear ratio ensures the speed reduction rate required by the driver. The first vehicle of the present invention totally controls both the transmission and the motor, thereby implementing the braking in response to the specification by the driver in a wide range.
The braking control with the torque of the motor generally works when the accelerator pedal is released. In the case where the power-source braking does not attain the sufficient speed reduction rate corresponding to the requirement of the driver, the driver should step on the brake pedal, so as to make the wheel braking act and raise the speed reduction rate. This requires the driver to change the foot position from the accelerator pedal to the brake pedal. A return of the foot position from the brake pedal to the accelerator pedal is then required for acceleration following the speed reduction. The frequent change of the foot position worsens the controllability of the vehicle.
The first vehicle of the present invention, on the other hand, implements the braking control with the motor in a wide range of speed reduction rate as described above. A simple release of the accelerator pedal accordingly ensures the sufficient speed reduction rate that is substantially coincident with the requirement of the driver. The driver can thus brake the vehicle and subsequently accelerate the vehicle without changing the foot position between the accelerator pedal and the brake pedal. From this point of view, the first vehicle of the present invention significantly improves the controllability of the vehicle.
The first vehicle of the present invention also has advantages on the energy efficiency as discussed below. The wheel braking utilizes the friction of the brake pad against the drive shaft and abandons the kinetic energy of the vehicle in the form of thermal energy, so as to brake the vehicle. This is not desirable from the viewpoint of energy efficiency. The regenerative braking by means of the motor, on the other hand, regenerates the kinetic energy of the vehicle in the form of electric power. This structure enables the regenerated energy to be effectively used for a subsequent drive. The first vehicle of the present invention implements the regenerative braking by means of the motor in a wide range, thereby significantly improving the energy efficiency of the vehicle.
The term xe2x80x98speed reduction ratexe2x80x99 in the specification hereof represents a parameter relating to the speed reduction of the vehicle. The speed reduction rate may be, for example, a deceleration, that is, a reduction rate of vehicle speed per unit time, or a braking force.
The term xe2x80x98vehiclexe2x80x99 in the specification hereof includes various types of vehicles. The first type is a vehicle having only the motor as the power source, that is, a pure electric vehicle. The second type is a hybrid vehicle having both the engine and the motor as the power source. The hybrid vehicle includes a parallel hybrid vehicle where the power output from the engine is transmitted directly to the drive shaft and a series hybrid vehicle where the power output from the engine is not directly transmitted to the drive shaft but is used only for generation of electric power. The principle of the present invention is applicable to both the parallel hybrid vehicle and the series hybrid vehicle. The present invention is also applicable to the structure having three or more engines or motors as the power source. The third type is a vehicle using only the engine for the power source of drive but also having the motor mounted thereon for the purpose of regenerative braking.
The vehicle of the present invention may further include a braking power source that applies a braking torque, other than the motor. In the vehicle with only the motor as the braking power source, the motor driving state specification unit sets the torque of the motor to attain all the desired speed reduction rate. In this case, a negative torque is generally set to the motor torque, and the motor carries out regenerative operation. In the vehicle with a plurality of braking power sources including the motor, on the other hand, the motor driving state specification unit sets the torque of the motor by taking into account the speed reduction rate attained by the other braking power sources. In this case, the speed reduction rate by the other braking power sources may be fixed to a predetermined value. Alternatively the motor torque may be subjected to feedback control, which makes the total speed reduction rate equal to a predetermined value.
The technique of the present invention is applicable to a diversity of vehicles having various structures.
The technique of the present invention is especially preferably applied to the vehicle further having an engine in a specific state of linkage that enables a braking torque to be applied to the drive shaft. In this structure, the selection unit selects the target gear ratio, based on the torques of the motor and the engine, and the motor driving state specification unit specifies the target driving state of the motor by taking into account the braking torque applied by the engine. The vehicle may be a hybrid vehicle that can use the motor for a drive or alternatively a vehicle that uses the motor only for the purposes other than a drive, for example, regenerative braking.
The hybrid vehicle typically has a motor as an auxiliary power source in addition to the engine. The motor is used, for example, at a start of the vehicle or during a low-speed drive and is utilized to supplement the insufficient torque of the engine. The parallel hybrid vehicle often has a small-sized motor having a relatively low rated output suitable for such purposes. In many cases, the motor mounted on the hybrid vehicle does not have the ability to sufficiently carry out the regenerative braking required by the driver.
The conventional vehicle using the motor not for a drive but for the other purposes, such as the regenerative braking, often has the small-sized motor, as in the case of the hybrid vehicle. The technique of the present invention ensures the braking control in a wide range by controlling both the transmission and the motor.
This technique is especially effective in the vehicles with the motor of the limited rating.
In the first vehicle of the present invention, the target gear ratio is selected by a variety of methods.
In accordance with one preferable embodiment, the vehicle further includes a storage unit, in which a relationship between the target speed reduction rate and the target gear ratio is stored. The selection unit selects the target gear ratio by referring to the storage unit.
In this arrangement, the relationship between the target speed reduction rate and the gear ratio is flexibly specified by taking into account the structure of the vehicle, the available range of the gear ratio by the transmission, and the rated output of the motor. This arrangement facilitates the selection of the target gear ratio in the braking process and accordingly reduces the load of the processing.
The relationship between the target speed reduction rate and the gear ratio may be specified by a diversity of settings, based on experiments or analyses. For example, the gear ratio may be set unequivocally corresponding to each target speed reduction rate, or alternatively a plurality of gear ratios may be mapped to each target speed reduction rate. In one example of the latter case, two gear ratios are allocated to each target speed reduction rate. This arrangement advantageously enables the selection of the more appropriate gear ratio by taking into account a variety of conditions other than the speed reduction rate, for example, the driving state of the vehicle.
One embodiment changes the relationship between the speed reduction rate and the minimum gear ratio used in each driving state of the vehicle, among the relations between the gear ratio and the speed reduction rate, in response to the specification by the driver. The stationary drive generally adopts the minimum gear ratio. When the driver tries to change the setting of the speed reduction rate, the driver often intends to change the speed reduction rate during the stationary drive, that is, to change the speed reduction rate at the minimum gear ratio. The arrangement of varying only the setting of the speed reduction rate at the minimum gear ratio simplifies the control procedure for attaining the speed reduction rate in response to the operation by the driver. In the case where the available gear ratio range is changed according to the driving state of the vehicle, the setting of the speed reduction rate may be varied only at the minimum gear ratio among the available gear ratios in each driving state.
Another embodiment varies not only the setting of the speed reduction rate at the minimum gear ratio but the speed reduction rate at all the gear ratios used in each driving state of the vehicle. In the case where the available gear ratio range is changed according to the driving state of the vehicle, the setting of the speed reduction rate at a certain gear ratio may not be fixed but be varied with the change of the available gear ratio range. For example, the speed reduction rate at the third speed in the case of a drive using the first through the fifth speeds may be different from the speed reduction rate at the third speed in the case of a drive using only the first through the third speeds.
The arrangement of varying only the speed reduction rate at the minimum gear ratio may be combined with the arrangement of varying the speed reduction rate at all the gear ratios. One exemplified control of such combination varies only the setting of the speed reduction rate at the fifth speed, which represents the minimum gear ratio, in the case of a drive using the first through the fifth speeds. The control varies the setting of the speed reduction rate at all the gear ratios in the case of a drive using only the first through the third speeds.
When the vehicle has a shift mechanism that enables the driver to change the available gear ratio range used during a drive, the speed reduction rate reflecting the requirement of the driver can be attained according to the selection of the shift mechanism. The shift mechanism may have a manual mode that allows the driver to manually change the gear ratio. In the case where the change of the gear ratio is manually implemented, the driver often requires the flexible braking and acceleration of the vehicle. In this case, the speed reduction rate may be changed to a larger value than the value selected in the case of the automatic control of the gear ratio.
In the first vehicle of the present invention, a variety of structures may be applied to the operation unit, through an operation of which the driver specifies the speed reduction rate in the process of braking with the motor.
In accordance with one embodiment, when the vehicle includes a changeover unit that changes over a selectable gear ratio range for the target gear ratio in response to a predetermined operation by the driver of the vehicle, the operation unit has a mechanism that ensures the specification of the speed reduction rate in response to another operation of the changeover unit that is different from the predetermined operation for the changeover.
This arrangement enables the target speed reduction rate to be set without unnecessarily providing any additional switch or related element in the vehicle. The changeover unit is generally disposed in a location that ensures the easy access of the driver. The operation unit of this structure accordingly has excellent controllability in the process of setting the speed reduction rate. The operation unit shares the structure with the conventionally provided changeover unit. The driver can thus set the speed reduction rate without feeling any incompatibility.
There is another advantage in the arrangement that the operation unit for setting the speed reduction rate shares the structure with the changeover unit for changing over the selectable gear ratio range. The first vehicle of the present invention controls both the gear ratio of the transmission and the regenerative braking of the motor, thereby attaining the braking control in a wide range of speed reduction rate. In the arrangement that the changeover unit and the operation unit are designed to have separate mechanisms, there is a possibility that the currently set target speed reduction rate is not attained in the gear ratio range selected by the operation of the changeover unit. In the vehicle of the above arrangement that the changeover unit and the operation unit are designed to share a common mechanism, however, such conflicting instructions are readily avoided. This arrangement accordingly ensures the adequate braking control.
A gearshift lever employed in the vehicle with a conventional automatic transmission is applicable for the changeover unit. In this case, the operation unit may be actualized by the structure that causes the gearshift lever to be operated in a movable area, which is different from a conventional movable area to changeover the available range of the change-speed gear. In accordance with one concrete structure, when a gearshift lever, which is slid along a predetermined groove to changeover the available range of the change-speed gear, is used for the changeover unit, the operation unit is constructed as a mechanism where the gearshift lever is slid along a second groove, which is provided in parallel with the predetermined groove, to set the speed reduction rate. In another example, the operation unit is constructed as a mechanism where the gearshift lever is slid along a rearward extension of the predetermined groove to set the speed reduction rate. In still another example, the speed reduction rate may be set by sliding the gearshift lever while keeping a preset switch on the gearshift lever in a pressed position, or by sliding the gearshift lever that is kept in a pull-up position or in a press-down position.
In some vehicles with the automatic transmission mounted thereon, the changeover unit may be provided on a steering wheel. In accordance with one embodiment, pressing a first switch provided on the steering wheel widens the available range of the change-speed gear in the automatic transmission, whereas pressing a second switch narrows the range. The operation unit of the present invention may utilize the structure of this changeover unit. For example, the speed reduction rate may be increased by a press of the first switch and decreased by a press of the second switch. The vehicle having the changeover unit provided on the steering wheel also has a gearshift lever; in general. In the case where the gearshift lever is in a predetermined position to set the target speed reduction rate, the first switch and the second switch function to set the speed reduction rate. In other cases, the first switch and the second switch function to changeover the available range of the change-speed gear in the automatic transmission. The use of the switches provided on the steering wheel advantageously enables the driver to quickly set the speed reduction rate while holding the steering wheel for a drive.
In accordance with one preferable application of the present invention, the operation unit included in the first vehicle has a mechanism that specifies the speed reduction rate by sliding a lever along a slide groove formed in advance. In this application, the mechanism of the operation unit may allow the setting of the speed reduction rate to be varied continuously according to a sliding operation of the lever. The operation unit may be constructed to share the structure with a mechanism for inputting a gearshift position that represents a selectable gear ratio range during a drive of the vehicle. The lever for setting the speed reduction rate may alternatively be provided separately from the mechanism for inputting the gearshift position.
In accordance with one preferable embodiment, the operation unit includes a first slide groove, along which the lever is slid during the drive of the vehicle, and a second slide groove, along which the lever is slid to specify the speed reduction rate, wherein the first slide groove and the second slide groove are disposed in series. In this embodiment, the operation unit may have a mechanism that increases the speed reduction rate with an increase in deviation from a movable range of the lever during the driver of the vehicle. In accordance with another preferable embodiment, the operation unit includes a first slide groove, along which the lever is slid during the drive of the vehicle, and a second slide groove, along which the lever is slid to specify the speed reduction rate, wherein the first slide groove and the second slide groove are disposed in parallel.
In the first vehicle of the present invention, a diversity of arrangements may be applied to set the target speed reduction rate.
In accordance with a first arrangement, the target speed reduction rate setting unit includes: a detection unit that measures a number of times of operation of the operation unit; and a unit that sets the target speed reduction rate in a stepwise manner according to the observed number of times of operation.
The first arrangement enables the moderate setting of the target speed reduction rate. The stepwise variation in target speed reduction rate enables the driver to change the target speed reduction rate in a wide range by an operation that requires only a relatively short time period. This arrangement thus ensures the excellent operatability.
In accordance with a second arrangement, the target speed reduction setting unit includes: a detection unit that measures an operation time of the operation unit; and a unit that sets the target speed reduction rate according to the observed operation time.
In the second arrangement, the target speed reduction rate may be varied relative to the operation time in a stepwise manner or alternatively in a continuous manner. In the latter case, the target speed reduction rate may be varied proportional to the operation time or non-linearly relative to the operation time. In one example, the target speed reduction rate may be varied relatively gently at the beginning of the operation and be quickly changed after elapse of a preset time period.
In any case, the target speed reduction rate setting unit of the second arrangement enables the target speed reduction rate to be set by one action, thereby ensuring the excellent operatability. The structure of continuously varying the target speed reduction rate according to the operation time ensures the minute setting of the target speed reduction rate reflecting the requirement of the driver.
In accordance with a third arrangement, the target speed reduction setting unit includes: a detection unit that measures a quantity of operation of the operation unit; and a unit that sets the target speed reduction rate according to the observed quantity of operation.
In the third arrangement, the target speed reduction rate may be varied relative to the quantity of operation in a stepwise manner or alternatively in a continuous manner. In any case, the target speed reduction rate setting unit of the third arrangement enables the driver to intuitively recognize the relationship between the operation and the speed reduction rate. The first through the third arrangements discussed above may be applied alone or in combination.
In accordance with one preferable application of the present invention, the first vehicle further includes: a switch that gives an instruction to execute braking with the specified speed reduction rate in response to a predetermined operation by the driver of the vehicle;
and a permission unit that allows operations of all the target speed reduction rate setting unit, the selection unit, the motor driving state specification unit, and the control unit only in the case where the braking execution instruction is given by means of the switch. In the vehicle of this application, the operation of the switch switches on and off the braking control with the specified speed reduction rate, that is, the currently set target speed reduction rate. When the switch is in ON position, the braking control is executed with the speed reduction rate specified by the driver. When the switch is in OFF position, on the other hand, braking is carried out with a predetermined speed reduction rate, irrespective of the specification of the speed reduction rate. This arrangement enables the driver to be clearly conscious of the execution of the braking control with the speed reduction rate corresponding to the desired setting of the driver. The driver can thus continue driving without feeling any incompatibility by the power source braking.
A diversity of structures may be applied for the switch.
In accordance with one embodiment, the vehicle further includes a changeover unit that changes over a selectable gear ratio range for the target gear ratio in response to a predetermined operation by the driver of the vehicle. In this structure, the switch has a mechanism that gives the braking execution instruction in response to another operation of the changeover unit that is different from the predetermined operation for the changeover.
This arrangement enables the on-off instruction regarding the execution of the braking control with the specified speed reduction rate to be given without unnecessarily providing any additional switch or related element in the vehicle. The changeover unit is generally disposed in a location that ensures the easy access of the driver. This arrangement thus ensures the excellent on-off operatability of the switch. The switch shares the structure with the conventionally provided changeover unit. The driver can thus carry out the switch operations without feeling any remarkable incompatibility.
In the case where a gearshift lever is applied for the changeover unit, for example, the switch-on and -off operations may be carried out by operating the gearshift lever in a movable area, which is different from a conventional movable area to changeover the available range of the change-speed gear. In accordance with one concrete structure, when a gearshift lever, which is slid along a predetermined groove to changeover the available range of the change-speed gear, is used for the changeover unit, the gearshift lever is moved in a direction crossing the predetermined groove, so as to set the switch in ON position or in OFF position. The switch may share the structure with the operation unit for setting the speed reduction rate. In this case, one applicable design causes the switch to be set in ON position by moving the gearshift lever to a specific position where the gearshift lever functions as the operation unit discussed above. This arrangement actualizes the switch that has the excellent operatability and makes the driver feel lesser incompatible, while ensuring the setting of the target speed reduction rate.
In accordance with another preferable application of the first vehicle of the present invention, the target speed reduction rate setting unit includes: a decision unit that determines whether the operation of the operation unit is valid or invalid; and a prohibition unit that prohibits the setting of the target speed reduction rate from being changed when it is determined that the operation is invalid.
The vehicle of this arrangement effectively prevents the setting of the target speed reduction rate from being changed by a wrong, unintentional operation of the driver. This arrangement thus prevents the braking control against the requirement of the driver and improves the controllability and the driving stability of the first vehicle of the present invention. This prohibition unit is especially effective in the case where the operation unit for changing the setting of the speed reduction rate is provided on a specific part that allows an unintentional touch of the driver, for example, on a steering wheel.
A variety of modifications may be applied for this arrangement.
In accordance with one embodiment, in the case where the operation unit has a mechanism that allows the driver to give an instruction to increase the speed reduction rate simultaneously with an instruction to decrease the speed reduction rate, the decision unit determines that the operation of the operation unit is invalid in the case where the increase instruction is given simultaneously with the decrease instruction.
In the vehicle with the switch for giving the instruction to execute braking with the specified speed reduction rate as discussed above, the decision unit may determine that the operation of the operation unit is invalid when the switch is in OFF position.
In the first vehicle of the present invention, the operation unit may set the speed reduction rate as an absolute value.
It is, however, preferable that the operation unit has a mechanism that gives an instruction to vary the speed reduction rate, and the target speed reduction rate setting unit varies the speed reduction rate relative to a preset initial speed reduction rate as a standard level, in response to the operation of the operation unit, thereby setting the target speed reduction rate.
This arrangement enables the driver to regulate the speed reduction rate as an addition to or a subtraction from the initial speed reduction rate, and thereby facilitates the setting of the adequate target speed reduction rate. In the structure of setting the speed reduction rate as an absolute value, it is difficult for the driver to select an appropriate numeral at the beginning. There is accordingly a possibility that the specified speed reduction rate is extremely low or high. The arrangement of regulating the speed reduction rate as an addition to or a subtraction from the initial speed reduction rate, on the other hand, effectively prevents the specified speed reduction rate from being extremely low or high against the requirement of the driver.
In this arrangement, a variety of settings may be applied for the initial speed reduction rate.
In the case where the first vehicle further includes: a switch that gives an instruction to execute braking with the specified speed reduction rate in response to a predetermined operation by the driver of the vehicle; a permission unit that allows operations of all the target speed reduction rate setting unit, the selection unit, the motor driving state specification unit, and the control unit in the case where the braking execution instruction is given; and an ordinary braking unit that carries out braking with a predetermined speed reduction rate, irrespective of the operation of the operation unit, in the case where the braking execution instruction is not given, the initial speed reduction rate may be set equal to the predetermined speed reduction rate employed by the ordinary braking unit.
This arrangement enables the driver to regulate the speed reduction rate relative to, as the standard, the predetermined speed reduction rate employed in the process of ordinary braking. The driver can thus intuitively understand the relationship between the current setting and the actual speed reduction rate and thus readily set the adequate speed reduction rate. At the time point when the braking control with the specified speed reduction rate is switched on by the operation of the switch, the speed reduction rate is equal to the initial speed reduction rate, that is, the predetermined speed reduction rate employed in the process of ordinary braking. This effectively prevents the driver from feeling any shock due to the switch on-off operations. The vehicle of this arrangement ensures the on-off of the braking control with the specified speed reduction rate without making the driver and any passenger feel incompatible, and thereby attains a smooth drive.
The vehicle of the above arrangement may run while the switch is kept in ON position, that is, while the braking control with the currently set target speed reduction rate is kept on. Since the initial speed reduction rate is equal to the predetermined speed reduction rate employed in the process of ordinary braking, the driver can drive the vehicle with the switch kept in ON position without feeling any incompatibility. When the driver needs to adjust the speed reduction rate, this arrangement enables the speed reduction rate to be regulated quickly without the on operation of the switch.
In the vehicle having the above structure, the initial speed reduction rate may be set to be significantly greater than the predetermined speed reduction rate employed by the ordinary braking unit.
The driver generally feels the necessity of the adjustment of the speed reduction rate in the case where there is an insufficient speed reduction rate in the process of ordinary braking. The arrangement of setting the initial speed reduction rate to be significantly greater than the predetermined speed reduction rate employed in the process of ordinary braking enables the speed reduction rate desired by the driver to be attained quickly. An appropriate value, which has been determined according to the type of the vehicle, for example, based on experiments, may be set to the supplement of the predetermined speed reduction rate. Alternatively the driver may set a desired value reflecting the own feeling to the supplement by a predetermined operation.
In the structure that enables the speed reduction rate to be set relative to the predetermined initial speed reduction rate as the standard, it is preferable, that the target speed reduction rate setting unit includes: a cancellation decision unit that determines whether or not the target speed reduction rate is to be cancelled; and a setting cancellation unit that resets the target speed reduction rate to the initial speed reduction rate when it is determined that the target speed reduction rate is to be cancelled.
In the vehicle of this arrangement, the setting cancellation unit enables the setting of the target speed reduction rate to be readily returned to the initial speed reduction rate. For example, when the driver repeatedly carries out the operation for setting the target speed reduction rate and makes the current setting unclear, this arrangement enables the setting of the target speed reduction rate to be started all over again relative to the initial value as the standard. In the event that a value significantly deviating from the initial speed reduction rate is set to the target speed reduction rate, this arrangement enables the target speed reduction rate to be returned to the initial value quickly and readily, thereby ensuring the excellent controllability.
A variety of structures may be applied for the cancellation decision unit.
In accordance with one embodiment, when the first vehicle further includes a switch that gives an instruction to execute braking with the specified speed reduction rate in response to a predetermined operation by the driver of the vehicle, the cancellation decision unit determines that the target speed reduction rate is to be cancelled in response to an operation of the switch.
The setting may be cancelled when the position of the switch is changed from ON to OFF or vice versa, that is, from OFF to ON.
The driver often forgets the previous setting of the target speed reduction rate after a long time period has elapsed since the previous setting. Under such circumstances, if the braking control with the previously set target speed reduction rate is carried out in response to the on operation of the switch, there is a fair possibility that the braking control is carried out with the speed reduction rate unexpected by the driver. The above arrangement causes the target speed reduction rate to be returned to the initial value every time the switch is set in ON position. This effectively prevents the braking control against the requirement of the driver and thus ensures a drive of excellent driving stability without making the driver feel incompatible.
In accordance with another embodiment, when the first vehicle further includes a failure detection unit that detects a failure of the operation unit, the cancellation decision unit determines that the target speed reduction rate is to be cancelled in response to detection of the failure.
The arrangement of validating the setting of the target speed reduction rate under the failure condition may lead to the setting of an extremely high value or low value to the target speed reduction rate. The vehicle of the above arrangement effectively eliminates such possibility and ensures a drive of excellent driving stability without making the driver feel incompatible.
In accordance with still another preferable application of the first vehicle of the present invention, the selection unit selects the target gear ratio with preference to a preset initial value.
There may be a number of gear ratios that attain the speed reduction rate reflecting the requirement of the driver. The vehicle of the above arrangement sets the gear ratio with preference to the preset initial value. A variety of settings may be applied for the initial value. For example, the gear ratio suitable for acceleration following the braking control may be set to the initial value. In another example, the gear ratio that ensures a wide range of practical speed reduction rate may be set to the initial value. The above arrangement provides the vehicle with characteristics corresponding to the setting of the initial value and thus improves the controllability and the ride of the vehicle. There is generally some latitude in target speed reduction rate specified by the driver. In the case where the lower limit of the latitude is set to the target speed reduction rate, there are generally a large number of gear ratios that attain the target speed reduction rate. The arrangement of setting the gear ratio with preference to the preset initial value is thus especially effective in such cases.
In accordance with one embodiment, when the first vehicle further includes a switch that gives an on-off instruction to execute braking with the specified speed reduction rate in response to a predetermined operation by the driver of the vehicle, the preset initial value is equal to a previous gear ratio immediately before the braking execution instruction is given by means of the switch.
This arrangement ensures the braking control with the initial value set equal to the previous gear ratio immediately before the braking execution instruction is given by the operation of the switch. This prevents the gear ratio of the transmission from being changed in response to the on operation of the switch and thus ensures the braking control with the currently set target speed reduction rate without making the driver feel incompatible.
In accordance with another preferable application of the present invention, the first vehicle further includes an information unit that informs the driver of the currently set target speed reduction rate.
The information unit may inform the driver of the target speed reduction rate in the form of a visually recognizable display or in an aurally recognizable form. The informed target speed reduction rate may be an absolute value or a variation from a preset initial value.
When the vehicle includes the switch for giving the instruction to execute braking with the specified speed reduction rate, it is preferable that the vehicle has an information unit that informs the driver of a result of the instruction whether or not to execute the braking with the specified speed reduction rate.
This arrangement enables the driver to readily check the on-off state of the switch and thus effectively prevents wrong operations. The information unit may be a visual display or a sound alarm.
In accordance with still another preferable application of the present invention, the first vehicle further includes: a failure detection unit that detects a failure of the operation unit; and an information unit that informs the driver of detection of the failure.
The vehicle of this arrangement enables the driver to readily check the operation unit for a failure. The driver can thus continue driving without feeling any incompatibility even when the operation unit fails. The information unit may be a visual display, a sound alarm, or any other suitable form. In the vehicle having a display unit that displays the currently set speed reduction rate, the detection of a failure may be displayed in a different form, for example, in a flash, for the purpose of information.
In accordance with another preferable application of the present invention, the first vehicle further includes: a gearshift position input unit that inputs a gearshift position, which represents a selectable gear ratio range during a drive of the vehicle; and a storage unit in which speed reduction rates of the vehicle are stored in advance corresponding to gearshift positions. In this structure, the target speed reduction rate setting unit sets the target speed reduction rate in response to the operation of the operation unit and the input gearshift position by referring to the storage unit. The selection unit selects the target gear ratio that attains the target speed reduction rate with preference to an energy recovery rate in the course of braking, irrespective of the gearshift position.
In the vehicle of this arrangement, the gear ratio of the transmission used in the braking process is set with preference to the energy recovery rate, irrespective of the selectable gear ratio range specified by the gearshift position input unit. In the case where the advantageous gear ratio from the viewpoint of energy recovery is present out of the selectable gear ratio range specified by the driver, the vehicle of the above arrangement enables the braking control with the advantageous gear ratio. This arrangement enhances the energy recovery rate of the vehicle during the braking control. The energy recovery rate here represents an efficiency of regeneration carried out by the motor to regenerate the kinetic energy of the vehicle.
The vehicle of this arrangement attains the speed reduction rate previously set according to the gear ratio range. The driver specifies the selectable range of gear ratio, which leads to the braking control with the desired speed reduction rate. The gear ratio of the transmission during a drive of the vehicle is restricted in the selectable gear ratio range specified by the driver. This arrangement enables the vehicle to be quickly accelerated with an acceleration reflecting the requirement of the driver, after the braking control.
The vehicle of this arrangement allows selection of the gear ratio in the braking process out of the specified selectable gear ratio range, thus attaining the speed reduction and acceleration reflecting the requirement of the driver while enhancing the energy recovery rate of the vehicle. This improves the effectiveness of the power source braking and enhances the controllability of the vehicle.
In the structure of selecting the gear ratio with preference to the energy recovery rate, it is preferable that the first vehicle further includes: an accumulator unit; and a detection unit that measures a remaining charge of the accumulator unit. In this case, the selection unit selects the target gear ratio according to the observed remaining charge of the accumulator unit.
In the case where the accumulator unit has a relatively low remaining charge, the gear ratio is selected to increase the quantity of electric power regenerated from the kinetic energy of the vehicle. In the case where the accumulator has a relatively high remaining charge, on the other hand, the gear ratio is selected to decrease the quantity of regenerated electric power. This arrangement advantageously causes the remaining charge of the accumulator unit to be kept in a favorable state. The selection of the gear ratio with preference to the energy recovery rate is not synonymous with the selection of the gear ratio that gives the maximum quantity of regeneration, but means the selection of the gear ratio that ensures regeneration of an adequate quantity of energy according to the driving conditions of the vehicle.
It is also preferable that the selection unit selects the target gear ratio in a specific range that prevents an extreme change of driving condition of a power source of the vehicle in a transient time from braking control to another driving state of the vehicle.
In the vehicle of this arrangement, the gear ratio set with preference to the energy recovery rate is not selected unconditionally but is limited in a specific range. When the driver specifies the selectable gear ratio range, the gear ratio adopted for a drive following the braking control is within the selectable gear ratio range. In the case where the braking control is carried out with the gear ratio that significantly deviates from the specified gear ratio range, the gear ratio of the transmission is drastically changed in a transient time from the braking control to another driving state. The driving conditions of the power source are remarkably varied with the drastic change of the gear ratio. If the variation is extremely large, some troubles occur; for example, a significant vibration occurs in the vehicle or the driving state of the power source becomes unstable. In the vehicle of the above arrangement, the gear ratio is selected in the specific range that is set by taking into account the variation. This arrangement effectively prevents the occurrence of possible troubles in the transient time from the braking control to another driving state.
In the vehicle of the above arrangement, it is also preferable that the transmission attains a plurality of gear ratios set stepwise, and the selection unit selects the target gear ratio by allowing a deviation from the selectable gear ratio range corresponding to the input gearshift position by one step.
The vehicle of this arrangement facilitates the control of the transmission in the transient time from braking to another driving state. As described previously, when the driver specifies the selectable gear ratio range, the gear ratio adopted for a drive subsequent to the braking control is within the selectable gear ratio range. In the case where the braking control is carried out with the gear ratio that deviates from the specified gear ratio range by several steps, it is necessary to change the gear ratio of the transmission over the several steps in the transient period from the braking control to another driving state. The control actualizing such a change is undesirably complicated, and the change of the gear ratio may require a relatively long time. In the vehicle of the above arrangement, the selected gear ratio does not deviate from the specified gear ratio range by two or more steps. This arrangement avoids such complicated control and ensures the quick change of the gear ratio.
The present invention is also directed to a second vehicle that includes a motor connected with a drive shaft and is braked by means of a torque output from the motor. The second vehicle includes: an operation unit, through an operation of which a driver of the vehicle specifies a speed reduction rate in a process of braking with the motor; a target,speed reduction rate setting unit that sets a target speed reduction rate in response to the operation of the operation unit; a motor driving state specification unit that specifies a target driving state of the motor, in order to enable a braking force that attains the currently set target speed reduction rate to be applied to the drive shaft; a control unit that drives the motor in the specified target driving state; and a variation unit that varies a possible range of setting of the target speed reduction rate according to a driving condition of the vehicle.
In the second vehicle of the present invention, the possible range of setting of the target speed reduction rate is varied according to the driving conditions of the vehicle. This arrangement attains the adequate speed reduction rate according to the driving conditions and thereby significantly improves the controllability and the driving stability of he vehicle.
The possible range of the speed reduction rate, in which the vehicle is stably driven, varies according to the driving state of the vehicle. By way of example, in the case where the road surface has a very slippery condition, braking with a higher speed reduction rate than required may cause a slip or a skid of the vehicle. In another example, in the case where the traffic is heavy to make the distance between adjacent vehicles on the same traffic lane relatively narrow, braking with a lower speed reduction rate than required needs a change of the foot position to the brake pedal, in order to compensate for the insufficiency of the speed reduction rate. This may significantly damage the advantage of the power-source braking.
The second vehicle of the present invention changes the possible range of setting of the target speed reduction rate according to the driving conditions of the vehicle and thereby ensures the braking control with the adequate speed reduction rate corresponding to the current driving conditions. The second vehicle of the present invention thus enhances the driving stability of the vehicle.
Like the first vehicle discussed above, the second vehicle of the present invention may be an electric vehicle, a hybrid vehicle, or any other suitable vehicle.
In accordance with one preferable application of the present invention, the second vehicle further includes: a transmission that enables selection of a plurality of gear ratios in a process of power transmission; a selection unit that selects a target gear ratio among a plurality of available gear ratios, the target gear ratio enabling the currently set target speed reduction rate to be attained by the torque of the motor; and a transmission control unit that controls the transmission to attain the target gear ratio.
The selection unit selects an adequate gear ratio according to the speed reduction rate specified by the driver and the magnitude of the torque output from the motor. Controlling the target torque of the motor at the adequate gear ratio ensures the speed reduction rate required by the driver. The vehicle of the above arrangement totally controls both the transmission and the motor, thereby implementing the braking in response to the specification by the driver in a wide range.
The selection unit and the transmission control unit here represent the units that respectively carry out selection and control in a wide sense. The selection unit is not restricted to the unit that selects an only target gear ratio. When there are a plurality of gear ratios mapped to the target speed reduction rate, the selection unit may select an optimum gear ratio among the plurality of gear ratios or select all the plurality of gear ratios as the target gear ratio. The transmission control unit may omit the changeover control of the gear ratio in the case where the selected target gear ratio has already been attained.
As described previously, the technique of the present invention is applicable to a diversity of vehicles. The technique of the present invention is especially preferably applied to the vehicle further having an engine in a specific state of linkage that enables a power to be output to the drive shaft. In this structure, the motor driving state specification unit sets a target torque of the motor by taking into account a braking torque applied by the engine.
In this structure, it is preferable that the second vehicle has a connection mechanism that connects and disconnects transmission of power from the engine to the drive shaft. It is more preferable that the second vehicle further includes a connection mechanism control unit that controls the connection mechanism to disconnect the transmission of power between the engine and the drive shaft in a process of braking with the torque of the motor.
The vehicle of the present invention carries out braking with electric power regenerated by the motor. When the vehicle has an engine, a braking force is added by engine brake. The engine brake causes the rotational power of the drive shaft to be consumed by the pumping and the friction of the engine, so as to implement the braking control. The engine brake reduces the quantity of regenerated electric power corresponding to its braking force.
The vehicle of the above arrangement enables the transmission of power from the engine to the drive shaft to be connected and disconnected. Disconnection of the power transmission in the braking process increases the quantity of regenerated electric power, and ensures the effective use of the kinetic energy of the vehicle. The connection and disconnection of the power may be carried out manually. The unit for controlling the connection mechanism, however, preferably ensures the more appropriate regeneration of energy.
The connection mechanism of the power has another advantage, that is, regulation of the braking force by the motor and engine brake. While the connection mechanism is in a connected position to add the braking force from the engine to the drive shaft, the drive shaft receives both the braking force by the engine brake and the braking force by the regenerative braking with the motor. This gives a large total braking force. In the connected position of the connection mechanism, the braking force by the engine brake is continuously added to raise the lower limit of the total braking force. Setting the connection mechanism in a disconnected position is accordingly desirable when it is required to decrease the lower limit of the total braking force.
In the vehicle of the above arrangement, controlling the connection mechanism regulates the upper limit and the lower limit of the braking force applicable to the drive shaft. This ensures the adequate power source braking. When a large braking force is required, the foot braking is generally combined with the power source braking. From the viewpoints of energy efficiency and regulation of the lower limit of the power source braking, it is highly effective to set the connection mechanism in the disconnected position in the braking process. Such control is especially effective to prevent the occurrence of a slip or a skid as discussed later.
The vehicle having the connection mechanism of the power may further include the transmission, the selection unit, and the transmission control unit discussed above. In one structure of this case, setting the connection mechanism in the disconnected position causes the gear ratio to have no effects on the braking control. In other words, any value may be set to the gear ratio under such conditions. As mentioned previously, the selection unit and the transmission control unit of the present invention carry out the selection and the control in a wide sense. In the structure that causes the gear ratio to have no effects on the braking control, the selection unit selects all the gear ratios as the target gear ratio. In this case, since the target gear ratio has already been attained, the transmission control unit always omits the changeover control of the gear ratio.
In the second vehicle of the present invention, a variety of techniques may be applied to vary the possible range of setting of the target speed reduction rate. One available technique widens the possible range of setting of the target speed reduction rate when the vehicle is in a specific driving state that ensures the sufficient driving stability even under the condition of varying speed reduction rate in a wide range. Another available technique wholly shifts the possible range of setting of the target speed reduction rate. For example, when it is determined that the vehicle runs on a down slope, the possible range of setting of the target speed reduction rate is wholly shifted in an increasing direction.
In accordance with one preferable application of the second vehicle of the present invention, the variation unit for varying the possible range of setting of the target speed reduction rate includes: a decision unit that determines whether or not a restriction condition to restrict the target speed reduction rate is fulfilled; and a restriction unit that actually restricts the target speed reduction rate when the restriction condition is fulfilled.
This application narrows the possible range of setting of the target speed reduction rate.
The vehicle of the above arrangement effectively prevents the driver from setting an excessively large or small speed reduction rate than required, thereby improving the driving stability of the vehicle. The range of the speed reduction rate that ensures the sufficient driving stability of the vehicle often depends upon the driving state of the vehicle. In the vehicle of the above arrangement, the possible range of setting of the target speed reduction rate is varied flexibly and appropriately according to the driving state of the vehicle. The possible range of setting of the target speed reduction rate may be narrowed by lowering the upper limit or alternatively by raising the lower limit. Any appropriate method should be adopted according to the driving state of the vehicle.
In the second vehicle of the present invention, a variety of techniques are applicable to determine whether or not the target speed reduction rate is to be restricted.
In accordance with a first embodiment, the decision unit determines that the restriction condition is fulfilled when there is a slip occurring in driving wheels connected with the drive shaft.
Braking with a high speed reduction rate on a road surface having a relatively low friction coefficient, for example, the snow-covered road or the wet road, may cause a slip or a skid of the vehicle. A slip or a skid of the driving wheels may be set to the restriction condition. This prevents the occurrence of a slip or a skid and improves the driving stability of the vehicle.
The occurrence of a slip or a skid may be detected by a variety of methods. One available method measures the numbers of rotations of plural driving wheels and determines the occurrence of a slip or a skid when there is a difference of or over a preset level between the observed numbers of rotations of the respective driving wheels. The second vehicle of the present invention has the motor connected with the drive shaft, so that the occurrence of a slip or a skid may be determined by variations of the torque and the revolving speed of the motor. In a vehicle with an acceleration sensor mounted thereon, the occurrence of a slip or a skid may be determined, based on the output of the acceleration sensor. The determination of the occurrence of a slip or a skid may be carried out not only at the time of braking but at the time of ordinary driving.
In accordance with a second embodiment, the decision unit carries out the determination, based on an operation of a switch that gives an instruction to restrict the possible range of setting of the target speed reduction rate.
In the vehicle of the above configuration, the driver intentionally operates the switch to restrict the possible range of setting of the target speed reduction rate. For example, when determining that the road surface has a relatively low friction coefficient, the driver operates the switch to prevent the possible occurrence of a slip or a skid. This arrangement thus further improves the driving stability of the vehicle. The switch here is different from the operation unit, through an operation of which the driver specifies the speed reduction rate. The operation of the switch enables the driver to change the setting of the speed reduction rate without a fear of the occurrence of a slip or a skid.
The switch here is not restricted to the above switch that is operated when the driver determines that the road surface has a relatively low friction coefficient. Other switches may be provided for a variety of purposes. The target speed reduction rate may be restricted in response to ON position of the switch or alternatively in response to OFF position of the switch. The target speed reduction rate may be restricted in a stepwise manner in response to the operation of the switch.
The restriction of the target speed reduction rate may be carried out under a variety of conditions. For example, in a vehicle having a specific sensor that measures the distances from adjacent vehicles on the same traffic lane, the target speed reduction rate is restricted, based on the distance of or below a predetermined level set as the restriction condition. In another example, in a vehicle having a specific apparatus that verifies the position of the vehicle in topography, the target speed reduction rate is restricted according to the variation in height of the road, on which the vehicle runs.
A variety of methods are applicable to restrict the target speed reduction rate. One method wholly restricts the variation of the target speed reduction rate relative to each quantity of operation of the operation unit for specifying the speed reduction rate. This arrangement leads to a gentler variation of the target speed reduction rate per unit quantity of operation of the operation unit.
In accordance with another preferable embodiment, the restriction unit restricts the target speed reduction rate to be not higher than a predetermined upper limit.
This arrangement advantageously facilitates the restriction of the target speed reduction rate. The variation of the target speed reduction rate per unit quantity of operation of the operation unit is fixed, irrespective of restriction or non-restriction of the target speed reduction rate. The driver can thus readily set the desired speed reduction rate.
In accordance with still another preferable embodiment, the restriction unit carries out feedback control to restrict the target speed reduction rate until the restriction condition becomes unfulfilled.
This arrangement restricts the target speed reduction rate to a specific range where the restriction condition is not fulfilled, thus further improving the driving stability of the vehicle. This arrangement does not reduce the speed reduction rate unnecessarily. For example, it is assumed that the occurrence of a slip or a skid of the driving wheels is set to the condition for restricting the target speed reduction rate. The speed reduction rate that prevents the occurrence of a slip or a skid depends upon the friction coefficient of the road surface. In the vehicle that carries out the restriction through the feedback control, the target speed reduction rate is gradually lowered until no occurrence of a slip or a skid is assured. This arrangement effectively prevents the occurrence of a slip or a skid without reducing the target speed reduction rate unnecessarily.
Although the above description regards the case of restricting the target speed reduction rate, any of the above applications may be adopted in the vehicle having a unit of extending the target speed reduction rate.
In accordance with another preferable application of the present invention, the second vehicle further includes an information unit that informs the driver of a variation in possible range of setting of the target speed reduction rate.
This arrangement enables the driver to drive the vehicle without feeling any incompatibility. The information unit may inform the driver of the widened range of setting of the target speed reduction rate or the narrowed range of setting of the target speed reduction rate. In the former case, the driver recognizes that the speed reduction rate may be set in a wider range, and drives the vehicle with a desired speed reduction rate. In the latter case, the driver is informed of the possibility that the specified speed reduction rate is not attained. This arrangement favorably reduces the incompatible feeling of the driver and the fear of a possible failure in the braking process.
The information unit may be a visual display or a sound alarm. In the vehicle having a display unit that displays the speed reduction rate set by the driver, the varied range of the target speed reduction rate may be displayed in a different form, for example, in a flash, for the purpose of information.
In any of the vehicles with the transmission discussed above, the following procedure may be applied to set and regulate the gear ratio.
The motor and the torque may be designed to have a plurality of combinations that attain a predetermined speed reduction rate at a preset vehicle speed, among a variety of combinations of the torque of the power source and the gear ratio of the transmission. Namely there are a plurality of combinations that attain the predetermined target speed reduction rate at the preset vehicle speed. This arrangement ensures the braking control with an optimum combination according to the driving state of the vehicle, and accordingly allows the braking with the motor to be utilized in a wide range of driving conditions.
In the case where both the motor and the engine can be utilized for braking, it is desirable that the plurality of combinations include those corresponding to the regenerative operation of the motor and those corresponding to the power operation of the motor.
When the vehicle has an engine as the power source, the braking control may be carried out with the torques of both the motor and the engine. According to the gear ratio, the braking torque of the engine may be insufficient or excess to the desired speed reduction rate. In the former case, the motor performs the regenerative operation to supplement the insufficiency of the speed reduction rate, so as to implement the desired braking control. In the latter case, the motor performs the power operation to ensure the braking control with the desired speed reduction rate. Even when a relatively small gear ratio is adopted for a drive, the braking control with the motor carrying out the regenerative operation enables the desired speed reduction rate to be attained without the changeover of the gear ratio, thus ensuring a smooth drive. The braking control with the motor carrying out the power operation during a drive, on the other hand, advantageously enables the quick acceleration subsequent to the deceleration.
In the above structure, the selection of the gear ratio is carried out, for example, based on the remaining charge of the accumulator unit. It is here assumed that there are a plurality of target gear ratios. One exemplified procedure selects a gear ratio corresponding to the power operation of the motor in the case where the remaining charge is not less than a predetermined level, while otherwise selecting a gear ratio corresponding to the regenerative operation of the motor. This arrangement enables the braking control to be carried out with the combination corresponding to the power operation of the motor, when the accumulator unit has the remaining charge close to its full charge level. The vehicle of such arrangement thus carries out the braking control with the motor, irrespective of the charge level of the accumulator unit.
The technique of the present invention is also actualized by a method of controlling operation of any of the vehicles discussed above.